Method of making porous inorganic bodies

ABSTRACT

This invention relates to the production of porous bodies of silica (SiO2), alumina (Al2O3), titania (TiO2), and zirconia (ZrO2) having a skeletal density approximating theoretical density of the metal oxide, a high pore volume, a high wall porosity, and a very narrow range of pore distribution. The process involves reacting the metal oxide particles with a liquid binder selected from the group consisting of acetic acid, sodium acetate, magnesium acetate, zinc acetate, and propionic acid, drying, and firing the mixture at a temperature below that at which the material sinters.

United States Patent [1 Messing METHOD OF MAKING POROUS INORGANIC BODIES [75] lnventor: Ralph A. Messing, l-lorseheads, N.Y.

[73] Assignee: Corning Glass Works, Corning,

[22] Filed: Mar. 26, 1973 [21] App]. No.: 344,964

[52] US. Cl 106/41; 106/40 R; 106/73.3; l06/73.4; 106/73.5 [51] Int. Cl. C03c 11/00 [58] Field of Search 106/40 R, 41, 39.5, 40 V, 106/73.3, 73.4, 73.5; 264/43, 44

[56] References Cited UNITED STATES PATENTS 3,347,798 lO/1967 Baer et a1. 264/44 x 3,598,618 8/1971 Fujii et a1 106/40 R FOREIGN PATENTS OR APPLICATIONS 1,062,410 3/1967 United Kingdom 106/40 R [l 1] 3,892,580 [4 11 July 1, 1975 Primary Examiner-Winston A. Douglas Assistant Examiner-John F. Niebling Aztorney, Agent, or FirmJames A. Giblin; Clinton S. .lanes, Jr.; Clarence R. Patty, Jr,

[ 7 ABSTRACT propionic acid, drying, and firing the mixture at a temperature below that at which the material sinters.

6 Claims, No Drawings METHOD OF MAKING POROUS INORGANIC BODIES The utility of particles having high surface areas due, at least in part, to inherent high porosity has been constantly increasing in recent years in such diverse appli cations as catalyst supports, filter media, and as carriers in chromatographic columns. Still another area which has experienced almost explosive activity within the past few years is the development of a wide variety of immobilized enzyme composites. The present invention provides porous bodies which are especially useful in that field.

Enzymes have frequently been termed natures catalysts and are complex organic substances, usuallyproteins such as amylase and pepsin, which accelerate (catalyze) specific chemical transformation, as in the digestion of foods in plants and animals. Over 700 enzymes have been studied and classified by various researchers throughout the world, this classification being based upon the type of reaction or the material (substrate) acted upon. Most enzymes exhibit long chain, complicated structures with high molecular weights and are commonly soluble in water. This solubility of enzymes in water has limited the utility thereof for some applications inasmuch as their removal from reaction media is rendered difficult with consequent adverse effects upon the purity of the final product. Furthermore, and very importantly economically, soluble enzymes can be used only once ina batchtype reaction. Therefore, because of the high costs frequently involved with many enzymes, the use of enzymes on a large industrial scale was severely limited even'though their utility as extremely active catalysts was wellrecognized. Consequently, numerous techniques have been contrived to immobilize, insolubilize, or stabilize enzymes by attaching or bonding them to carrier materials which are insoluble in water in such a manner that the enzyme is rendered immobile but is available to exercise its catalytic activity. Theterms insoluble" and insolubilized denote enzymes which have been made essentially insoluble in water through attachment to, or entrapment within, a water-insoluble carrier material. lmmobile and immobilized refer to enzymes which have insolubilized in such a manner that the shape or conformation thereof necessary for catalysis has been retained. Finally, the expressions stable and stabilized denote enzymes which exhibit significant retention of enzymatic activity or the ability to catalyze reactions over an extended period of time. Hence, the focal point of all these techniques has been to provide means for presenting enzymes within a reaction environment whereby the catalytic activity thereof could be enjoyed in successive reactions over a prolonged span of time rather than a single batchtype reaction process.

U.S. Pat. No. 3,556,945 discloses the adsorption of enzymes to a variety of siliceous materials having available surface silanol groups. US. Pat. No. 3,519,528 describes means for chemically coupling enzymes to an essentially limitless variety of inorganic materials through the mechanism of silane coupling agents. In

quantity of enzyme which can be adsorbed to a porous glass and the surface area and pore size therein.

However, US. application Ser. No. 227,205, filed Feb. 17, 1972 now US. Pat. No. 3,783,101 in the names of William H. Tomb and Howard H. Weetall, explains that siliceous carriers, such as porous glass, are not highly durable in basic environments. This circumstance limits the utility thereof at those pH values where many enzymes are at their most active. That invention describes the coating of siliceous carriers with an alkali-durable metal oxide.

US. application Ser. No. 332,807, now US. Pat. No. 3,850,751 filed Feb. 16, 1973 in the name of Ralph A. Messing, describes the effectiveness of certain nonsiliceous, water-insoluble carrier materials demonstrating excellent alkaline durability. These materials were selected from the group of alumina (A1 0 titania (TiO and zirconia (ZrO That invention demanded porous materials of high surface area having an average pore diameter at least as large as the largest dimension of the enzyme to be bonded thereto, but less than 1000A. Theminimum useful pore size is that which will permit entry of the enzyme into the internal porous network and mass diffusion of the enzyme throughout the pores. The maximum size of 1000A is dictated by a decrease in the surface area of the carrier resulting from larger pores and by the fact that there is a reduction in the amount of protection which the rigid pores can provide for the enzyme against a turbulent reaction environment.

lt'can be readily recognized that the most efficient enzyme utilization will be possible where the pores are carefully controlled to match the size of the enzyme to be attached to the internal pore surface and this size maintained with good uniformity. Hence, a uniform pore size will insure entry of the enzyme into the pores and avoid loss thereof from the pores in the turbulent reaction environment.

The largest dimension of a particular enzyme can be determined approximately by conventional means from its molecular weight or by exclusion techniques. In the case of enzymes exhibiting a spherical configuration,

- the-largest dimension will approach the diameter of the molecule. With the more common enzymes having an elongate structure, the largest dimension will approximate the length of the enzyme. In general, most enaveraging about 100A to 500A. Nevertheless, it must view of the requirement for extremely high surfacearea 1 for loading the enzymes, porous glass particles or beads have been employed in both of these methods for en'- zyme attachment. A paper by R. A. Messing in EN ZYMOLOGIA, 39, pp. 12-14 (1970) provides a brief discussion of the relationship existing between the zymes can be effectively bonded within the pores of 'carriers wherein the average pore diameter ranges between about 100A to 1000A, with the preferred values be re-emphasized that the ideal average pore size exhibited by the carrier is directly dependent upon the size of enzyme to be bonded therewithin.

Therefore, the primary object of the present invention is to provide a method for making porous bodies of A1 0 TiO ZrO and, optionally, SiO wherein the pore diameter ranges between about 100A to 1000A and wherein the skeletal density of the porous body approaches the theoretical density of the inorganic oxide, the pore volume and wall porosity are high, and the pore size varies only within a relatively narrow range, viz., at least about percent fall within i 10 percent of the average value.

The basis of the present porous body technology contemplates the joining together of particles having controlled dimensions. In simplest terms, the porous bodies of the instant invention are made by mixing a liquid 3 binder solution with the inorganic oxides to yield a mixture of a uniform consistency. This mixture is then dried and fired at a temperature below the sintering temperature of the inorganic oxide.

as spray drying, drum drying, or the use of vacuum are obviously also quitefeasible. Finally, the dry green bodies are fired at elevated temperatures to develop a chemical bond between the oxide particles. A temperature of at least 450C. has been found necessary for this It can readily be appreciated that the liquid binder employed should not dissolve or substantially erode the step with the range of 500600C being preferred. inorganic oxide particles lest they will no longer permit Temperatures up to 800C. have been satisfactorily utithe achievement of a controlled pore dimension which lized but such high temperatures demand extreme cauis a function of the initial particle size. Such a circumtion to avoid destruction of the pores through sintering stance essentially eliminates the common mineral of the material. In the main, firing the green bodies for acids, e.g., HF, l-lCl, H SO HNO etc., from considerabout l-3 hours at 500600C. has yielded eminently ation. Yet, some surface reaction between the particles satisfactory porous bodies. and the binder is required to cause the joining together Table I records a group of particulate inorganic oxof the particles. The present invention is founded upon ides which were employed in the following working exthe unique utility of acetic acid, propionic acid, sodium amples along with several physical properties thereof: acetate, magnesium acetate, and zinc acetate as binders for the inorganic oxide particles A1 0 TiO ZrO S10 and mixtures thereof. I TABLE I The general technique utilized for the preparation of the porous bodies of this invention involves three steps.

Particle Surface Area The first comprises combining the oxide particles with oxide Diameter (A) (meter lgram) Density (gram/cc.) the binder solution at room temperature or at a slightly I elevated temperature, e.g., up to about 60 C., but 2:62 Ag; 23 2:3 below that at which substantial volatilrzation Wlll occur o 210 5 5 5 and definitely below the boiling point of the aqueous 550 50 solutions employed. Lower temperatures down to the freezing point of the solutions can be utilized also, of course, but are normally less convenient than simply Table II reports the binder solutions employed, the performing the mixing at room temperature and do not amounts of each utilized, and the particulate oxide mayield any improvement in the final body. The resultant terial combined therewith to yield the porous bodies slurry of particles and binder is then dried, preferably listed in Table III. Each of porous bodies was prepared at an elevated temperature approaching the boiling by mixing the aqueous binder solution with the oxide point of the solution, e.g., 90l00C., although lower particles. The pH of each slurry was determined after temperatures can be used for longer periods. Normally, the samples had achieved a stable pH value. The samthe drying is undertaken at temperatures below the ples were dried in air at 90l00C. overnight and boiling point of the solution to eliminate the hazard of thereafter fired at 525C.550C. for about 1-2 hours. the particles being violently agitated as the water is vig- After cooling to room temperature, the bodies were orously expelled. Whereas simple air drying for several submitted for porosimetry analyses utilizing mercury hours is normally employed, more rapid methods such intrusion.

TABLE II Example Binder Al O TiO ZrO SiO No. Binder Solution Volume (ml.) (grams) (grams) (grams) (grams) 1 0.lM Acetic Acid l7 l0 2 Distilled Water 150 35 3 Distilled Water l7 l0 4 0.1M Sodium Acetate l7 l0 5 0.lM Formic Acid l7 l0 6 0.lM Propionic Acid l7 l0 7 Distilled Water* l7 l0 8 0.1M Acetic Acid 17 l0 9 'Distilled Water 17 l0 10 0.1 Sodium Acetate l7 l0 ll 0.1 Formic Acid l7 l0 12 0.1 Propionic Acid 17 l0 l3 Distilled Water l7 10 l4 0.lM Acetic Acid l7 10 l5 Distilled Water 17 l0 l6 0.lM Sodium Acetate l7 l0 17 0.lM Propionic Acid .17 l0 l8 0.lM Acetic Acid 17 l0 l9 Distilled Water 17 1O 20 0.lM Sodium Acetate l7 l0 2] 0.lM Formic Acid 17 IO 22 0.lM Propionic Acid l7 IO 23 Distilled Water*** l7 l0 24 0.lM Magnesium Acetate 32 1O 25 1.66M Zinc Acetate 200 60 26 0.lM Magnesium Acetate 325 27 0.lM Magnesium Acetate 325 lOO *Added I.() ml 0.lN HCl and 0.5 ml lN HCI. pH adjusted to 4.07

Added 0.l6 ml lN HCI and 0.8 ml 0.lN HCl. pH adjusted to 3.18 ""Added 0.5 ml 0.lN HCl. pH adjusted to 2.57

Furthermore, whereas aqueous solutions have been employed in the examples above as a matter of convenience and in the interest of economy, it will be appreciated that non-aqueous solvents such as ethanol and TABLE III Pore Skeletal Wall Pore Diameter in A Example Volume Density Porosity No. pH (cc/g) (g/cc) Maxi- Average Minimum Comments mum 1 4.05 0.579 3.372 67.8 200 175 140 Excellent-high density and porosityless than 5% of pore diameters outside of desired average range 2 4.00 0.670 2.141 64.6 450 320 220 Poorlow density and pore size varied quite widely from average range 3 4.22 0.578 2.436 60.5 200 180 140 Poorlow density and wall porosity-pore size varied quite widely from average range 4 4.85 0.612 2.974 67.1 200 180 140 Good-high porosity and less than 10% of pore diameters outside of desired average-density slightly low 5 4.01 0.555 1.457 48.9 200 160 140 Por-low density and porositypore size nonuniform 6 4.01 0.571 3.432 67.2 200 180 120 Excellent-high density and porosity-less than of pore diameters outside of desired average range 7 4.07 0.578 1.313 46.5 200 160 120 Poorlow density and porosity-pore size nonuniform 8 2.93 0.375 3.960 61.4 288 275 220 Excellenthigh density and wall porosity-less than 5% of pore diameters outside of desired averagerange 9 4.57 0.403 3.396 59.3 350 300 220 Poor-low density and nonunifonn pore size 10 6.10 0.447 3.372 61.8 440 350 200 Fair-high porosity but low density and about 10% of pore diameters outside of desired average range 1 l 2.51 0.405 1.197 34.1 300 270 180 Poorlow density and porosity with nonuniform pore size 12 2.99 0.429 3.232 58.9 300 270 220 Fair-low density but high wall porosity and less than 10% of pore diameters outside of desired average range 13 3.18 0.349 3.760 57.5 300 250 200 P oor-high density but low porosity and nonuniform pore size 14 1.73 0.214 5.674 57.7 190 175 150 Excellent-high density and porosity-less than 5% of pore diameters outside of desired average 15 2.40 0.236 4.995 55.2 190 180 150 Poor-low density and porosity 16 5.51 0.321 5.349 65.0 240 220 160 Good-high density and porosity-Jess than 10% of pore diameters outside of desired average range 17 0.306 5.265 62.3 200 180 160 Good-high density and porosity-less than 10% of pore diameters outside of desired average range 18 2.88 0.910 1.894 65.5 900 450 250 Fair-high density and porosity but greater than 10% of pore diameters are outside desired average range 19 3.71 0.769 1.651 59.5 870 450 260 Poor-low density and porosity with nonuniform pore size 20 6.02 0.808 2.100 65.3 680 510 350 Excellent-high density and porosity with less than 5% of pore diameters outside desired average range 21 2.39 0.936 0.851 48.0 875 500 225 Poor-low density and porosity with nonuniform pore size 22 2.88 0.954 1.785 64.0 800 500 220 Fair-fair density and porosity and greater than 10% of ore diameters outside desired average ran e 23 2.57 1.006 1.070 52.5 900 480 180 oor-low density and porosity with nonuniform pore size 24 6.25 0.872 1.566 60.4 875 550 350 Good-high porosity with less than about 10% pore diameters outside desired average range 25 0.830 2.080 67.0 875 675 400 Goodhigh density and porosity with less than about 10% of pore diameters outside desired average range 26 5.69 0.601 3.019 69.5 250 200 145 Excellenthigh density and porosity with less than about 5% of pore diameters outside desired average range 27 6.29 0.571 3.580 68.9 450 350 220 Excellent-high density and porosity with less than about Table III clearly illustrates that acidity of solution alone is not responsible for permitting the production of porous bodies having the desired uniformity of pore size. Thus, Examples 7, l3, and 23 provided slurries wherein the pH varied throughout the acid range but the resultant products exhibited poor quality. Hence, the acetic acid, propionic acid, magnesium acetate, and zinc acetate enter into some special reaction with the A1 0 TiO ZrO and SiO particles to yield the uniformly porous articles of the invention.

Although 0.1M aqueous solutions of the binder materials were employed in the above-described examples, it will be appreciated that the concentrations thereof can be varied more-or-less essentially at will provided that care is taken not to dissolve the inorganic oxides. Of course, very dilute solutions will require longer exposure periods to react with the particulate material. In general, solutions between about 0.01M-2M have proven very satisfactory.

5% of pore diameters outside desired average range methylethyl ketone can also be employed. These solvents are frequently more rapid evaporating than water and, therefore, their use can reduce the time required for drying. However, they also may require more careful handling due to their ready combustion.

Finally, a combination of Table I with Table III demonstrates that the average pore diameter of the porous body can be controlled by exercising care in selecting the particle size of the original inorganic oxide. Hence, the average pore size of the porous product will approximate the size of the starting particles. Conversely, then, to secure porous bodies containing pores having diameters ranging between about l00A-l000A will generally require the use of inorganic oxide particles varying in size between about l00A-l000A.

It has been further observed that the surface area of the porous body does not differ markedly from that of the base inorganic oxide particles, as is evidenced in the following two examples.

EXAMPLE *28- To 170 ml of 0.1M acetic acid in a 400 ml beaker,-

100 grams of the Ti reported in Table I were added with stirring and gentle heating to 40C. over a fifteen minute interval. The beaker with the slurry was placed in an oven to dry overnight at 95C. The sample was then fired for 70 minutes in a furnace operating at 525C. Porosimetry analysis indicated a pore volume of 0.4 cc/g, a wallporosity of 59.4 percent, a minimum pore diameter of 200A, a maximum pore diameter of 350A, and an average pore diameter of 300A with less than percent of the pore diameters outside of the desired average range. The body had a surface area of 5 1' meters /g.

The particle diameter of the starting TiO material was 320A and the surface area was 48 meters lg.

EXAMPLE 29 To 34 ml. of0.lM acetic acid in a 100 ml. beaker, 20 grams of ZrO were added with stirring. The sample was oven dried overnight at 100C, and subsequently fired for three hours in a furnace operating at 525C. The porous body exhibited the following characteristics: a surface area of 54 meters lg, a pore volume of 0.24 cc/g, a wall porosity of 60.4 percent, a minimum pore diameter of 170A. Less than 5 percent of the pore diameters were outside of the desired average range.

The particle diameter ofthe starting ZrO material was 210A and the surface area thereof was 50 meter /g.

I claim: i I

l. A method for producing porous bodies from Al- O TiO ZrO SiO and mixtures thereof having pore diameters ranging between about lOOA-lOOOA,

wherein the skeletal density of the porous body approaches the theoretical density of the oxide and at least about 90 percent of the pores have pore diameters which fall within i 10 percent of theavera ge pore diameter value, which comprises:

a. forming a slurry consisting of particulate A1 0 TiO ZrO SiO and mixtures thereof, wherein they particle diameters thereof approximate the desired average pore diameter and range between about l00A l0O0A, ;a'n d a solution selected from the group consisting of acetic acid, propionic acid, magnesium acetate, zinc acetate, and sodium acetate;

b. drying said slurry; and

c. firing the dried material at about 450-800C.

2. A method according to claim 1 wherein said slurry is made utilizing a solution at temperatures ranging be- 

1. A METHOD FOR PRODUCING POROUS BODIES FROM AL203, TI02, ZRO2, SIO2, AND MIXTURES THEREOF HAVING PORE DIAMETERS RANGING BETWEEN ABOUT 100A-1000A, WHEREIN THE SKELETAL DENSITY OF THE POROUS BODY APPROACHES THE THEORETICAL DENSITY OF THE OXIDE AND AT LEAST ABOUT 90 PERCENT OF THE PORES HAVE PORE DIAMETERS WHICH FALL WITHIN $ 10 PERCENT OF THE AVERAGE PORE DIAMETER VALUE, WHICH COMPRISES: A. FORMING A SLURRY CONSISTING OF PARTICULATE AL2O3, TIO2 ZRO2, SIO2, AND MIXTURES THEREOF, WHEREIN THE PARTICLE DIAMETERS THEREOF APPROXIMATE THE DESIRED AVERAGE PORE DIAMETER AND RANGE BETWEEN ABOUT 100A-1000A, AND A SOLUTION SELECTED FROM THE GROUP CONSISTING OF ACETIC ACID, PROPIONIC ACID, MAGNESIUM ACETATE, ZINC ACETATE, AND SODIUM ACETATE, B. DRYING SAID SLURRY, AND C. FIRING THE DRIED MATERIAL AT ABOUT 450*-800*C.
 2. A method according to claim 1 wherein said slurry is made utilizing a solution at temperatures ranging between the freezing point anD boiling point thereof.
 3. A method according to claim 1 wherein said solution is an aqueous solution.
 4. A method according to claim 3 wherein said acetic acid, propionic acid, magnesium acetate, zinc acetate, and sodium acetate are present in amounts ranging between about 0.01-2M.
 5. A method according to claim 1 wherein said drying is carried out at temperatures between the freezing point and boiling point of the solution.
 6. A method according to claim 1 wherein said firing is carried out at a temperature between about 500*-600*C. 